Many silicone oils that give a refreshing sensation at the time of application have been developed and used in skin treatment compositions.
However, since ultraviolet absorbents and drugs do not dissolve well in silicone oils, the addition of hydrocarbon oil components in which drugs and ultraviolet absorbents dissolve well has been desired.
While the hydrocarbon oil components dissolve drugs and ultraviolet absorbents well, they have a problem in that stickiness tends to result with higher blend ratios.
In view of the aforementioned problem, the inventors conducted earnest research and discovered that alkyl benzoate having a specific structure can be added to a skin treatment composition to provide a skin treatment composition that gives a superior refreshing sensation at the time of application, and can contain drugs and ultraviolet absorbents in a stable manner, and thus completed the present invention.
The object of the present invention is to provide a skin treatment composition that gives a superior refreshing sensation at the time of application and can contain slightly soluble ultraviolet absorbents and drugs in a stable manner.
In a sunblock cosmetic consisting of a water-in-oil type emulsified composition, the oil phase is the continuous phase (outer phase). Therefore, compared with a sunblock cosmetic consisting of a oil-in-water type emulsified composition, it has a higher resistance to microorganisms. Also, at the time of application, it leaves an oil film with a low moisture permeability that protects the skin from drying for a long time. Furthermore, it doesn't re-emulsify easily when exposed to water in situations including bathing, washing/cleaning, and perspiration. For these reasons, it is used as a base agent in sunblock cosmetics.
However, conventional sunblock cosmetics consisting of a water-in-oil type emulsified composition must dissolve a large amount of a highly polar ultraviolet absorbent in the oil phase, resulting in separation and aggregation over a period of time; hence there is the problem of poor long term stability.
Also, in terms of usability, compared with a oil-in-water type sunblock cosmetic, it has problems such as stickiness, oiliness, and poor spreadability.
In view of the aforementioned problems, what has been desired is the development of an oil component that has a superior ability to dissolve a highly polar ultraviolet absorbent and a water-in-oil type emulsification base agent that can stably emulsify the oil phase containing an ultraviolet absorbent.
In view of the aforementioned problem, the inventors conducted earnest research and discovered that alkyl benzoate having a specific structure can be used as an oil component to dissolve the ultraviolet absorbent and an ester bond product of polyhydroxystearic acid having a specific structure can be used for the emulsifier to prepare a water-in-oil type emulsified composition that gives a refreshing sensation without stickiness at the time of application and has superior long term stability, and thus completed the present invention.
The object of the present invention is to provide a sunblock cosmetic consisting of a water-in-oil type composition that is not sticky, gives a refreshing sensation at the time of application, and can stably contain a highly polar ultraviolet absorbent, which has been difficult to introduce in a stable manner.